What is the way to increase certainty in Allah, especially with low motivation and the feeling that Satan is exploiting this weakness?

To increase one's faith, strength, certainty in Allah Almighty, and trust in Him, it is recommended to consistently perform the obligatory duties (Fara'id), increase in supererogatory acts (Nawafil), engage in the remembrance of Allah Almighty, ponder over His verses, and reflect on His creations. This is supported by the words of Allah Almighty: "Indeed, the believers are those who, when Allah is mentioned, their hearts tremble, and when His verses are recited to them, it increases them in faith; and upon their Lord they rely. Those who establish prayer and from what We have provided them, they spend. Those are the believers, truly. For them are degrees with their Lord and forgiveness and noble provision" [Al-Anfal: 2-4], and His saying: "Unquestionably, [for] the allies of Allah there will be no fear concerning them, nor will they grieve Those who believed and used to fear Allah" [Yunus: 62-63].

It is also mentioned in a Hadith Qudsi that Allah Almighty said: "Whoever shows enmity to a friend of Mine, I shall be at war with him. My servant does not draw near to Me with anything more beloved to Me than what I have enjoined upon him. And My servant continues to draw near to Me with supererogatory deeds until I love him. When I love him, I am his hearing with which he hears, his sight with which he sees, his hand with which he strikes, and his foot with which he walks. If he asks Me, I will surely give him, and if he seeks refuge in Me, I will surely grant him refuge."

It is also advisable to read the biographies of Allah's allies among the prophets and believers to emulate them, to leave no room for the whispers of Satan, to seek refuge in Allah from him, and to occupy oneself with the remembrance of Allah and obedience to Him.